Edexcel Chemistry Unit 2 Revision.

7/30/2019 Edexcel Chemistry Unit 2 Revision.

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Alkanes and Alkenes

ALKANES;- Single covalent bonds

- Saturated hydrocarbons no spare single bonds,

- Dont decolourise bromine water no spare bonds

- Wont form polymers no spare bonds

- The first four Alkanes are;

*Methane CH4

*Ethane C2

H6

*Propane C3H8

* Butane C4H10

ONE E SINGLE BOND TIMES BY TWO AND PLUS TWO.

Double the amount of Carbon

and + 2 = The amount of

Hydrogen

ALKANES One E = 1

covalent bond.


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ALKENES;

- Double covalent bonds

- Unsaturated hydrocarbons have spare double bonds- Will decolourise bromine water have spare bonds

- Form polymers by polymerisation

- The first two Alkenes are;* Ethene C2H4

* Propene CH6

DOUBLE E FOR DOUBLE BONDAND YOU TIMES BY TWO ONLY. FOR THIS JUST

REMEMBER THE NUMBER 2

Amount of Carbon x 2 = Amount

Of Hydrogen

ALKENES 2 Es = 2 covalent

bonds


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Cracking Hydrocarbons

Long chain hydrocarbons are thick liquids, they are

not useful - the process called cracking makes

shorter chains, which are much more useful.

CONDITIONS NEEDED; Heat & A Catalyst


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Vegetable Oils

Vegetable Oils Unsaturated (have double bonds)

Polyunsaturated oils are the healthiest and

saturated oils are the least healthiest, because of

what they do to the amount of cholesterol in yourblood


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Unsaturated Oils are Runnier than Saturated Ones.

- The double bonds change

the shape of molecules bymaking an inflexible kink

in the carbon chain

- Kinked & less flexible

chains cant pack togetheras tightly as straighter,

flexible chains so the

forces between the

molecules arent as strong

- Weaker forces make oils

less viscous (less thick). So

unsaturated oils are

runnier than saturated oils


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Vegetable Oils are Hydrogenated for the Food Industry

Unsaturated Oils (ones with double bonds) can be changed tosaturated oils by breaking a double bond and adding

hydrogen = this is called hydrogenation

A Nickel Catalyst is needed it is a solid, so can be filtered out

and used again As the filtered oil cools down to room temperature it turns

into a solid fat (fat oil that is solid at room temp)

Polyunsaturated vegetable oils are hydrogenated to make

margarine. Not all the double bonds in the oil arehydrogenated, so some of the margarine is still unsaturated

its called a partially hydrogenated oil. Firm enough to spread

yet still low in saturates compared to butter.


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Plastics

Plastics are long chain molecules called polymers

Polymers are made up of lots of monomers

The name of the plastic comes from the name of the

monomer, just put POLY in front

The use of a plastic depends on its properties, E.g. a

disposable cups for hot drinks needs to be of a low

cost and needs to have a high melting point


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CONDITIONS; High Pressure & Catalyst

Polymerisation Double Bonds are removed, SingleBonds are attached to the side of the first and last

Carbon.

Polymerisation


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Properties Of Plastics

THERMOPLASTIC;

They have very weak bonds between chains

These weak forces are really easy toovercome, so its easy to melt the plastic,

When it cools, the thermoplastic hardens into

a new shape. You can melt these plastic andremould them as many times as you like

E.g. Polythene


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THERMOSETTING;

They have crosslinks between chains these

hold the chains together in a solid structureThe polymer doesnt soften when its heated

but too much heat makes it burn

Thermosetting polymers decompose afterbeing heated

E.g. Bakelite


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Plastics Dont Rot

Most Plastics are non biodegradable

there not broken down by microorganisms

So they full up landfill sites

And you cant burn them as they give off toxic

gases

So what are we going to do with the 2 million

tonnes of plastic waste brits produce?


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Drug Synthesis

New drugs have to be safe. They go through many

stages of testing;

1 - Tests on living cells and animals to ensure the drug

works2 - Then tested on healthy humans

3 - Then tested on humans with the disease

4 A large group of people are tested, but some peopleare given a placebo.

PLACEBO a harmless tablet without the drug inside.


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Staged Synthesis

Helps you out how many products are to be produced

E.g.

A1, A2 + B1,B2,B3,B4,B5+ C

1,C2,C3

2As + 5Bs + 3Cs = 10 possible combinations


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Relative Formula Mass

Relative Atomic Mass (Ar);

He4

2

The TOP Number is

The Ar. So 4, Itsthe Relative

Atomic Mass (Ar)


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Relative Formula Mass (Mr);

Used For Compounds

Just Add All The Ars Of All The ElementsE.g.

MgCl

24 + (35.5 x 2) = 95

95, Is The Mr


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Empirical Formulae

How to work it out;

1) List all the elements

2) Write the experimental masses

3) Divide the experimental mass by the Ar

4) Turn the numbers into ratios, via x or

5) Get the ratio in its simplest form


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Calculating Masses in Reactions

Three Steps;

1) Write out the balanced equation

2) Work out the Mr just for the 2 substances

3) Apply the rule; divide to get one, then multiply to

get all


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E.g.

What mass of Magnesium Oxide is produced when 60gof Magnesium is burned in air?

1) Write out the balanced equation

2Mg +02 = 2MgO

2 ) Work out The Mr

Mg 2 x 24 = 24 & Mg0 2 x (24x16) = 803) Apply the rule; divide to get one, then times to get

all

48g of Mg . . . 80g of MgO

1g of Mg . . . 1.67g of MgO

60g of Mg . . . 100g of MgO

Divide by 48Divide

by 48

x 60x 60


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Atom Economy

Atom economy = total Mr of useful products

total Mr of reactants

High atom economy is better for profits and the

environment

X 100


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Percentage YieldPercentage Yield actual yield (g)

theoretical yield (g)

Actual what you get in practise

Theoretical predictionYields are always less than 100% because;

1) The reaction is reversible

2) Some particles may be lost during filtration

3) You ALWAYS lose a bit of liquid when transferring it

4) Impurities


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IsotopesISOTOPES different atomic forms of the same

element, which have the same number of

protons but different numbers of neutrons

Carbon 12 Carbon 14

C C6 protons

6 electrons

6 neutrons

6 protons

6 electrons

8 neutrons

12

6

14

6


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Periodic TableDmitri Mendleev first made it in 1869 ... Now there's around 100 element with more still

being discovered

Modern periodic table shows elements in order of

increasing atomic number It is laid out so that elements with similar properties

from columns

Elements in the a group have the same number ofouter electrons; E.g. All the elements in group 6,have six electrons in its outer shell, so they need 2electrons to be stable


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Electron Shells1st Shell 2 Electrons

2nd Shell 8 Electrons

3rd Shell 8 Electrons

4th

Shell 18 ElectronsUse the Atomic Number to work out the Electron Configuration;

O16

8So Oxygen has anelectron configuration of;

2,6


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Ionic BondingIonic Bonding Transferring Electrons

All elements want to lose/gain electrons to have a full outershell they want to be stable.

Groups 1 & 2 and 6 & 7 are most likely to form ions;

1&2; are metals and they lose electrons to form +ions orcations

6&7; are non-metals they gain electrons to form-ions oranions

When any cations react with anions they form ionic bonds,only elements of opposite sides of the periodic table withform ionic bonds


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When a atom loses a electron it

becomes POSITIVE because there

are more positives (protons) thannegative (electrons).

When a atom gains an electron itbecomes NEGATIVE because there

are more negatives electrons) than

positives (protons)


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Ionic Compounds

Sodium Chloride (NaCl)The sodium atom gives up its outer electron becoming

a postive ion. The chlorine atom picks up the electron,

becoming a negative ion.


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Ionic Bonds; produce giant ionic structures,

the ions are closely packed and there are very

strong chemical bonds between all the ions. Asingle crystal of salt is one giant ionic lattice

that why salt crystals are cuboids

They have high melting and boiling points dueto the very strong chemical bonds

They dissolve to form solutions that conduct

electricity because the electrons are able to

freely move, they also conduct electricity

when molten


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Reactivity Trends

The inner shells provide shielding from the

attraction of the positive nucleus.

GROUP 1; as the atoms get bigger, the outer

electron is more easily lost. This makes the alkalimetals more reactive as you go down the group

GROUP 7; as the atoms get bigger, the extra

electron is harder to gain. This makes thehalogens less reactive as you go down the group


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Metals Metals consist of a giant structureTheyre good conductors of heat and electricity due

to the free electrons

They are malleable (they can hammered/rolled

permanently out of shape) because the layers of

atoms in the metal can slide over each other They have high melting and boiling points due to

the very strong metallic bonds

They are hard this can be measured by how easy

it is to dent to metal, the harder it is to dent; the

harder the metal Metals can be mixed together to produce alloys

the properties of the metal are changed, alloys are

usually harder. E.g. steel is an alloy of iron and about

1% carbon. Steel is stronger and less brittle than iron.


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Electrolysis & Half Equations

Means splitting up with electricity;

It requires a liquid to conduct theelectricity , called the electrolyte (ioniccompounds dissolved in water/molten)

POSTIVE ions are called ANIONSbecause theyre attracted to the

ANODE

NEGATIVE ions are called CATIONSbecause theyre attracted to the

CATHODE

Make sure the charges balance in eachhalf equation


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Covalent Bonding

Sharing Electrons, to ensure both have a full outer

shell, to make them stable. Examples;

Hydrogen, H2

Hydrogen atoms have just one

electron. They only need one more to

complete the first shell

H - H


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Molecular Substances; the Halogens

The forces of attraction between the molecules are

very weak causing low melting and boiling points

Most molecular substances are gases/liquids are

room temperature They dont conduct electricity because there are no

electrons

You can always tell a molecular substance from its

physical state; its mushy a liquid/gas or a easily

melted solid.

i l h i l l i ili


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Group 7

Elements

Atomic

Number

Colour Physical

State at

room temp

Melting

Point

Boiling

Point

Fluorine 9 yellow gas -220C -188C

Chlorine 17 green gas -120C -34C

Bromine 35 red brown liquid -7C 59C

Iodine 53 dark grey solid 114C 184C

The pattern in properties in the table can be explained because;- The halogens get bigger as you go down the group

- The bigger the halogen molecule the stronger the inter molecular force of attraction

- The stronger the forces, the more energy it takes to seperate the molecules, and so the

higher their melting and boiling points


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Giant Covalent Structures: Carbon

DIAMOND;

- Hardest natural substance

- Pure diamond is shiny, colourless and clearideal for jewellery

- Each carbon atom forms four covalent bondsin a very rigid giant covalent structure whichmakes the diamond really hard. This makesdiamonds great as cutting tools.

- There are lots of strong covalent bonds, so its

got very high melting and boiling points- It doesnt conduct electricity as there are no

free electrons

GRAPHITE


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GRAPHITE

- Black, opaque and lustrous (kind of shiny)

- Each Carbon atom only forms threecovalent bonds creating sheets of carbonatoms which are free to slide over eachother

- The layers are held together loosely thatthey can be rubbed off onto paper thatis how a pencil works

- Graphite's got high melting and boilingpoints, the covalent bonds need lots ofenergy to break them

- As only 3 of carbons 4 outer electrons areused in bonds, there are lots of spareelectrons. This makes graphite a goodconductor of electricity


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Fullerenes

- Carbon can also form nanoparticlemolecules called Fullerenes. These aremolecules of carbon, shaped like hollow balls

or closed tubes- Each carbon atom form three covalent bonds,

leaving free electrons to conduct electrons

- The smallest fullerene is BuckminsterFullerene, which has 60 carbon atoms joinedin a ball its molecular formula is C60

- C60was discovered by chance. In the 1980s agroup of scientists investigating how carbonchains are formed in stars fired laser beams atgraphite discs. When they analysed the sootformed, they found clusters of 60 carbonatoms were surprisingly common


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Treatment and Homeopathy

Some people in the placebo control group will get betternaturally and others will feel better just because they thinktheyre being treated this is the placebo effect.

The main to look out for to decide whether a drug is effectiveor not is;

- Did the people taking the drug get better?

- Was the sample big enough? (testing 1000 people is betterthan testing 50)

- Did the study use a suitable control group

- How did the results from the control group compare withthe results from the group actually taking the drug? (If bothgroups got better the test proves nothing)


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Some Alternative Remedies arent Chemical-Based Homeopathic remedies contain highly diluted does of natural

substances that in their full-strength dose would produce the

symptoms of illness in a healthy person Remedies are made by extracting the active ingredient from a

plant, animal or mineral dissolving it in alcohol and thenprogressively diluting the mixture with water. A shakingprocess between each dilution is said to transfer the powers

of the ingredients to the water Homeopathic remedies dont have to go through the same

testing as conventional medicines the amounts of activeingredients are so low theyre considered harmless so therehave been very few large scale trails. A recent studycombining all the data gathered so far suggest that they workno better than a placebo, but many people still believe in thepower of homeopathy.


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Rates of ReactionSLOW REACTION; rusting of iron

MODERATE REACTION; a metal reacting with acid

FAST REACTION; explosion

The rate of a reaction depends on four things;

1) Temperature

2) Concentration (or pressure for gases)3) Catalyst

4) Size of Particles (or surface area)


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Measuring Rates Of ReactionRate of reaction = amount of reactant used/amount of product formed

time

Three different ways the speed can be measured;

PRECIPITATION; when the product of the reaction is a precipitate whichmakes the solution cloudy. Observe a marker through the solution andmeasure how long it takes to disappear and the quicker the marker

disappears the quicker the reaction. You could also use data-loggingequipment.

CHANGE IN MASS (USUALLY GAS GIVEN OFF); it can be carried out using amass balance. The quicker the reading on the balance drops, the faster thereaction. This is the most accurate method, but it had the disadvantage of

releasing gas straight into the roomTHE VOLUME OF GAS GIVEN OFF; it involves using a gas syringe to measure

the volume of gas given off. The more gas given off during a given timeinterval the faster the reaction. You have to be careful with the gassyringe, if you reaction is too vigorous, you can easily blow the plunger outthe end of the syringe.


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Collision Theory- When the temperature is increased the particles all move

quicker, if theyre moving quicker., theyre going to have morecollisions.

- If the solution is more concentrated, it means there are moreparticles of the reactant knocking about which makecollisions more likely.

- The particles around it in the solution with have more surfacearea to work onso therell be more useful collisions

- A solid catalyst gives reacting particles a surface to stick too.This increases the number of successful collisions by loweringthe activation energy

& MORE COLLISIONS INCREASE THE RATE OF REACTION

Faster collisions are ONLY caused by increasing he temperature


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Catalysts- They LOWER THE ACTIVATION ENERGY (the minimum

amount of energy needed for a reaction to happen). Itmakes it easier for reactions to happen and a lowertemperature can be used.

- Solid Catalysts work best when they have a big surfacearea to enable the reacting particles to meet us and dobusiness. Transition metals are common catalysts in theindustrial reactions

- An enzyme is a biological catalyst, enzymes need the

right temperature around 37C and ph 7 which isneutral, but pepsin (a stomach enzyme) works best atph2


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Energy Transfer in Reactions

ENERGY MUST ALWAYS BE SUPPLIED TO BREAK BONDS; during a

chemical reaction, all bonds are broken and new bonds are

formed. Energy must be supplied to break existing bonds so

bond breaking is ENDOTHERMIC. Energy is released when

new bond are formed, so bond formations is EXOTHERMIC.EXOTHERMIC; gives out energy, usually in the form of heat, E.g.

combustion and neutralisation reactions

ENDOTHERMIC; takes in energy usually in the form of heat, E.g.

Thermal decompositionEXO = EXIT energy exits

ENDO = ENTER energy enters


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Reversible ReactionsA reversible reaction is one where the products of the reaction can

themselves react to produce the original reactants

The sign showing a reversible reaction is;

Reversible Reactions will reach dynamic equilibrium this means that the

reactions are still taking place in both directions at the same rate, but the

overall effect is nil because the forward and reverse reactions cancel each

other out.

Changing the temperature & pressures, alter the position of equilibrium;

TEMPERATURE; all reactions are endothermic in one direction and exothermic

in the other direction. If you raise the temperature, the endothermic

reaction will use up extra heat. If you reduce the temperature, theexothermic reaction will give out more heat

PRESSURE; many reactions have a great volume on one side. If you raise the

pressure it will produce less volume. If you lower the pressure it will

produce more volume.


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Haber ProcessNitrogen + Hydrogen = Ammonia

N2(g) +3H2(g) 2NH3(g)Industrial Conditions; Pressure: 200 atmospheres Temperature: 450C Catalyst: Iron

- Higher pressures favour the forward reaction (since there are four molecules of gas on

the left for every 2 on the right)

- So the pressure is set as high as possible to give the best yeild without making theplant to expensive to build

- The forward reaction is exothermic so increasing the temp will move the equilibrium

the wrong way away from ammonia. So the yield of ammonia would be greater at a

lower temperature

- But lower temperature = slower rate of reaction- 450C is a compromise between maximum yield and speed of reaction

- The ammonia formed as a gas liquefies as it cools. The unused nitrogen and hydrogen

are reused

- The iron catalyst makes the reaction go faster & doesnt affect the yield

Ammonia makes Ammonium Nitrate Fertilizer;


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Ammonia makes Ammonium Nitrate Fertilizer;

If you neutralize ammonia with nitric acid, you get ammoniumnitrate. Ammonium nitrate is a good fertilizer as it has nitrogenfrom two sources.

Plants need nitrogen to make proteins Ammonium nitrate is much more effective than organic fertilizers

(e.g. pig poo)

There are disadvantages to artificial fertilizers;

- if they wash into streams they can set off a mega

growth/death/decay called eutrophication- if too many nitrates get into drinking water it can cause healthproblems as nitrates prevent bloody from carrying oxygen properlyand children can die from it

To help avoid these problems its important that artificial nitratefertilisers are applied carefully by all famers and they must notapply them if its likely to rain soon


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Basic ChemistryAq = aqueous. Where the solvent in the solution is water

Al2713ATOMIC NUMBER;

number of protons(number of electrons

is same as protons)

MASS NUMBER;

number of protons

and neutrons

Neutrons; 27 13 = 14Electrons ; 13

Protons; 13

Mass; 27

Edexcel Chemistry Unit 2 Revision.

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Transcript of Edexcel Chemistry Unit 2 Revision.